1. Field of the Invention
The present invention relates to well tools of the type having a mandrel telescopingly received within a housing and having a hydraulic metering means for metering a flow of fluid to impede movement of the mandrel within the housing so as to provide a time delay in such movement.
2. Description of the Prior Art
During the course of drilling an oil well, one operation which is often performed is to lower a testing string into the well to test the production capabilities of the hydrocarbon-producing underground formations intersected by the well. This testing is accomplished by lowering a string of pipe, commonly referred to as drill pipe, into the well with a formation tester valve attached to the lower end of the string of pipe and oriented in a closed position, and with a packer attached below the formation tester valve. This string of pipe with the attached testing equipment is generally referred to as a well test string.
Once the test string is lowered to the desired final position, the packer means is set to seal off the annulus between the test string and a well casing, and the formation tester valve is opened to allow the underground formation to produce through the test string.
One construction which is often used for operation of the formation tester valve, is an arrangement whereby the tester valve has a housing with a mandrel telescopingly received in the housing, and the valve of the tester valve is operated by setting down weight on the test string so as to telescopingly collapse the mandrel relative to the housing thereby opening the valve.
It is, however, necessary that the formation tester valve be able to transmit compressional hydraulic forces for relatively short periods of time without actuating the valve or closing the bypass port of the tool. This is necessary for a number of reasons. For example, when the well test string is being run into the well bore, the test string often encounters obstructions in the well bore and weight must be set down on the test string for a short period of time in order to push the test string past these obstructions. Also, once the test string is in its desired location, various tools located below the formation tester valve, such as for example the packer, often are designed to be actuated by setting weight on the test string.
Thus, it has been found desirable to provide such formation tester valves with a hydraulic time delay device which requires that sufficient weight be set down on the formation tester valve for a sufficient period of time, on the order of several minutes, before the formation tester valve will actually open.
An early example of such a formation tester valve with a hydraulic time delay is shown in U.S. Pat. No. 2,740,479 to Schwegman.
In Schwegman, the hydraulic time delay is provided by metering fluid through a plurality of tiny annular orifices created between metering pins 42 and metering passageways within which the metering pins are closely received.
Another example of a formation tester valve utilizing a hydraulic time delay is shown in U.S. Pat. No. 3,814,182 to Giroux, which in FIG. 10 thereof illustrates its hydraulic time delay device which meters fluid through a conically shaped annular passage defined between spaced conically tapered surfaces 124 and 125.
Also, it is well known in the prior art to utilize hydraulic impedance devices constructed by placing a fluid flow restricting orifice in a passageway between two fluid chambers. Examples of such devices are seen in U.S. Pat. No. 4,417,622 to Hyde, U.S. Pat. No. 3,664,415 to Wray et al., U.S. Pat. No. 4,113,012 to Evans et al., and U.S. Pat. No. 4,346,770 to Beck.